I am using QGIS to georeference B&W images. I have now done this and would like to set the black surround of the image (as a result of the georeferencing) to transparent but this does not work as bands 1,2 and 3 have the same values. I have noticed there is now a band 4 after georeferencing and would use this to drop out the black surround but I can only do this to bands 1,2 and 3.
I am not super experienced with rasters in QGIS so I am having difficulty determining if this question has been addressed.
This is a screen grab of the image I have, I am trying to remove the black triangles:
These are the values of the black surround:
These are the values of the black text and lines I would like to keep:
For anyone who reads this who might find this usefull I just worked out how to do it. I can set a band to be transparent. So I just set Band 4 to be transparent and it worked perfect.